To understand how T cells disengage from targets to allow serial killing, Stinchcombe et al. used peroxidase labeling of CD3ε and advanced imaging to follow TCR fates during interactions with target cells. T cell contact was initiated via lamellipodia, which flattened to form central supramolecular activation clusters (cSMACs). TCRs were observed to shed from the edges of receding cSMACs via budding ectosomes, which were taken up by the target cells. Ectocytosis appeared to be mediated through the membrane-curvature effects of diacylglycerol, produced upon TCR activation. TCR signal strength directly correlated with ectosome formation and T cell detachment.
Contributed by Ed Fritsch
ABSTRACT: Cytotoxic T lymphocytes (CTLs) kill virus-infected and cancer cells through T cell receptor (TCR) recognition. How CTLs terminate signaling and disengage to allow serial killing has remained a mystery. TCR activation triggers membrane specialization within the immune synapse, including the production of diacylglycerol (DAG), a lipid that can induce negative membrane curvature. We found that activated TCRs were shed into DAG-enriched ectosomes at the immune synapse rather than internalized through endocytosis, suggesting that DAG may contribute to the outward budding required for ectocytosis. Budding ectosomes were endocytosed directly by target cells, thereby terminating TCR signaling and simultaneously disengaging the CTL from the target cell to allow serial killing. Thus, ectocytosis renders TCR signaling self-limiting.
Author Info: (1) Cambridge Institute for Medical Research, Keith Peters Building, Cambridge CB2 0XY, UK. (2) Cambridge Institute for Medical Research, Keith Peters Building, Cambridge CB2 0XY,
Author Info: (1) Cambridge Institute for Medical Research, Keith Peters Building, Cambridge CB2 0XY, UK. (2) Cambridge Institute for Medical Research, Keith Peters Building, Cambridge CB2 0XY, UK. (3) Cambridge Institute for Medical Research, Keith Peters Building, Cambridge CB2 0XY, UK. (4) Max Planck Institute of Molecular Cell Biology and Genetics, 01307 Dresden, Germany. (5) The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK. (6) The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK. (7) Max Planck Institute of Molecular Cell Biology and Genetics, 01307 Dresden, Germany. (8) Cambridge Institute for Medical Research, Keith Peters Building, Cambridge CB2 0XY, UK.
